1. 载体崩溃 当出现硬件问题或文件系统出错，特别是硬盘损坏了，就没法保护数据安全了。另外，不同品牌的硬件和软件具有不同的持久保证的。总而言之，如果硬件或文件系统破坏了数据，MongoDB是无法保护数据的，这已经属于底层存储的事情了。可以使用复制来避
1. 载体崩溃
当出现硬件问题或文件系统出错，特别是硬盘损坏了，就没法保护数据安全了。另外，不同品牌的硬件和软件具有不同的持久保证的。 总而言之，如果硬件或文件系统破坏了数据，MongoDB是无法保护数据的，这已经属于底层存储的事情了。可以使用复制来避免这个问题，其实就是单点问题了。2. ?检查损坏
validate命令用来检测一个集合的损坏，如：> db.posts.validate({full:true})
{
"ns" : "ttlsa_com.posts",
"firstExtent" : "1:1036000 ns:ttlsa_com.posts",
"lastExtent" : "4:2000 ns:ttlsa_com.posts",
"extentCount" : 14,
"extents" : [
{
"loc" : "1:1036000",
"xnext" : "1:104e000",
"xprev" : "null",
"nsdiag" : "ttlsa_com.posts",
"size" : 61440,
"firstRecord" : "1:1037c30",
"lastRecord" : "1:103e4f0"
},
{
"loc" : "1:104e000",
"xnext" : "1:108a000",
"xprev" : "1:1036000",
"nsdiag" : "ttlsa_com.posts",
"size" : 245760,
"firstRecord" : "1:104e0b0",
"lastRecord" : "1:10556b0"
},
{
"loc" : "1:108a000",
"xnext" : "1:117a000",
"xprev" : "1:104e000",
"nsdiag" : "ttlsa_com.posts",
"size" : 983040,
"firstRecord" : "1:108a0b0",
"lastRecord" : "1:109a9b0"
},
{
"loc" : "1:117a000",
"xnext" : "1:155e000",
"xprev" : "1:108a000",
"nsdiag" : "ttlsa_com.posts",
"size" : 3932160,
"firstRecord" : "1:117a0b0",
"lastRecord" : "1:13739f0"
},
{
"loc" : "1:155e000",
"xnext" : "1:24ee000",
"xprev" : "1:117a000",
"nsdiag" : "ttlsa_com.posts",
"size" : 15728640,
"firstRecord" : "1:155e0b0",
"lastRecord" : "1:1bbe4f0"
},
{
"loc" : "1:24ee000",
"xnext" : "1:392e000",
"xprev" : "1:155e000",
"nsdiag" : "ttlsa_com.posts",
"size" : 21233664,
"firstRecord" : "1:24ee8b0",
"lastRecord" : "1:2b485b0"
},
{
"loc" : "1:392e000",
"xnext" : "1:56c5000",
"xprev" : "1:24ee000",
"nsdiag" : "ttlsa_com.posts",
"size" : 28667904,
"firstRecord" : "1:392e0b0",
"lastRecord" : "1:450dd30"
},
{
"loc" : "1:56c5000",
"xnext" : "2:2000",
"xprev" : "1:392e000",
"nsdiag" : "ttlsa_com.posts",
"size" : 38703104,
"firstRecord" : "1:56c50b0",
"lastRecord" : "1:617c0b0"
},
{
"loc" : "2:2000",
"xnext" : "2:3ad7000",
"xprev" : "1:56c5000",
"nsdiag" : "ttlsa_com.posts",
"size" : 52252672,
"firstRecord" : "2:20b0",
"lastRecord" : "2:188ac30"
},
{
"loc" : "2:3ad7000",
"xnext" : "2:7e1d000",
"xprev" : "2:2000",
"nsdiag" : "ttlsa_com.posts",
"size" : 70541312,
"firstRecord" : "2:3ad7470",
"lastRecord" : "2:66b8af0"
},
{
"loc" : "2:7e1d000",
"xnext" : "3:2000",
"xprev" : "2:3ad7000",
"nsdiag" : "ttlsa_com.posts",
"size" : 95232000,
"firstRecord" : "2:7e1d0b0",
"lastRecord" : "2:be8a2b0"
},
{
"loc" : "3:2000",
"xnext" : "3:dd21000",
"xprev" : "2:7e1d000",
"nsdiag" : "ttlsa_com.posts",
"size" : 128565248,
"firstRecord" : "3:20b0",
"lastRecord" : "3:63eb670"
},
{
"loc" : "3:dd21000",
"xnext" : "4:2000",
"xprev" : "3:2000",
"nsdiag" : "ttlsa_com.posts",
"size" : 173563904,
"firstRecord" : "3:dd210b0",
"lastRecord" : "3:12fccc30"
},
{
"loc" : "4:2000",
"xnext" : "null",
"xprev" : "3:dd21000",
"nsdiag" : "ttlsa_com.posts",
"size" : 234311680,
"firstRecord" : "4:20b0",
"lastRecord" : "4:7bec3b0"
}
],
"datasize" : 614217440,
"nrecords" : 305603,
"lastExtentSize" : 234311680,
"padding" : 1.0000000000221079,
"firstExtentDetails" : {
"loc" : "1:1036000",
"xnext" : "1:104e000",
"xprev" : "null",
"nsdiag" : "ttlsa_com.posts",
"size" : 61440,
"firstRecord" : "1:1037c30",
"lastRecord" : "1:103e4f0"
},
"lastExtentDetails" : {
"loc" : "4:2000",
"xnext" : "null",
"xprev" : "3:dd21000",
"nsdiag" : "ttlsa_com.posts",
"size" : 234311680,
"firstRecord" : "4:20b0",
"lastRecord" : "4:7bec3b0"
},
"objectsFound" : 305603,
"invalidObjects" : 0,
"bytesWithHeaders" : 619107088,
"bytesWithoutHeaders" : 614217440,
"deletedCount" : 125358,
"deletedSize" : 244912976,
"nIndexes" : 9,
"keysPerIndex" : {
"ttlsa_com.posts.$_id_" : 305603,
"ttlsa_com.posts.$index_doctorSn" : 305603,
"ttlsa_com.posts.$index_doctorUid" : 305603,
"ttlsa_com.posts.$index_hosDeptId" : 305603,
"ttlsa_com.posts.$index_hospitalId" : 305603,
"ttlsa_com.posts.$doctorNumberList_1_doctorOrderId_-1" : 305924,
"ttlsa_com.posts.$cityId_1_displayStatus_1" : 305603,
"ttlsa_com.posts.$standardDeptId_1_displayStatus_1" : 305603,
"ttlsa_com.posts.$doctorCode_1" : 305603
},
"valid" : true,
"errors" : [ ],
"ok" : 1
}
在上面输出底部，有个"valid" : true 说明没有损坏，如果不是，会找到一些损坏的细节。大部分输出是描述集合内部的结构，对于调试不是特别有用的。
只能检测集合，不能检测索引。
如果出现无效的BSONbj，通常就是损坏了。最糟糕的是出现pdfile，pdfile基本上是mongodb的数据存储核心，几乎可以判断数据文件已经损坏了。
如果出现损坏，会看到下面的日志信息：
Tue Dec 20 01:12:09 [initandlisten] Assertion: 10334:
Invalid BSONObj size: 285213831 (0x87040011)
first element: _id: ObjectId('4e5efa454b4ae20fa6000013')
如果第一个元素显示的是垃圾，不需要做什么。如果第一个元素是可见的，可以移除损坏的文档。如：
> db.remove({_id: ObjectId('4e5efa454b4ae20fa6000013')})
如果损坏并不局限于该文档，这种技术可能无法工作，你仍然需要进行修复。
3. 复制的持久性
复制集一个写可被回滚，直到它被写入到一个大多数的集合中。 > db.runCommand({"getLastError" : 1, "j" : true, "w" : "majority"}) 只能保证primary写入已经持久化，secondary未必持久化。原文地址：mongodb 持久化(3), 感谢原作者分享。
How does MySQL index cardinality affect query performance?Apr 14, 2025 am 12:18 AMMySQL index cardinality has a significant impact on query performance: 1. High cardinality index can more effectively narrow the data range and improve query efficiency; 2. Low cardinality index may lead to full table scanning and reduce query performance; 3. In joint index, high cardinality sequences should be placed in front to optimize query.
MySQL: Resources and Tutorials for New UsersApr 14, 2025 am 12:16 AMThe MySQL learning path includes basic knowledge, core concepts, usage examples, and optimization techniques. 1) Understand basic concepts such as tables, rows, columns, and SQL queries. 2) Learn the definition, working principles and advantages of MySQL. 3) Master basic CRUD operations and advanced usage, such as indexes and stored procedures. 4) Familiar with common error debugging and performance optimization suggestions, such as rational use of indexes and optimization queries. Through these steps, you will have a full grasp of the use and optimization of MySQL.
Real-World MySQL: Examples and Use CasesApr 14, 2025 am 12:15 AMMySQL's real-world applications include basic database design and complex query optimization. 1) Basic usage: used to store and manage user data, such as inserting, querying, updating and deleting user information. 2) Advanced usage: Handle complex business logic, such as order and inventory management of e-commerce platforms. 3) Performance optimization: Improve performance by rationally using indexes, partition tables and query caches.
SQL Commands in MySQL: Practical ExamplesApr 14, 2025 am 12:09 AMSQL commands in MySQL can be divided into categories such as DDL, DML, DQL, DCL, etc., and are used to create, modify, delete databases and tables, insert, update, delete data, and perform complex query operations. 1. Basic usage includes CREATETABLE creation table, INSERTINTO insert data, and SELECT query data. 2. Advanced usage involves JOIN for table joins, subqueries and GROUPBY for data aggregation. 3. Common errors such as syntax errors, data type mismatch and permission problems can be debugged through syntax checking, data type conversion and permission management. 4. Performance optimization suggestions include using indexes, avoiding full table scanning, optimizing JOIN operations and using transactions to ensure data consistency.
How does InnoDB handle ACID compliance?Apr 14, 2025 am 12:03 AMInnoDB achieves atomicity through undolog, consistency and isolation through locking mechanism and MVCC, and persistence through redolog. 1) Atomicity: Use undolog to record the original data to ensure that the transaction can be rolled back. 2) Consistency: Ensure the data consistency through row-level locking and MVCC. 3) Isolation: Supports multiple isolation levels, and REPEATABLEREAD is used by default. 4) Persistence: Use redolog to record modifications to ensure that data is saved for a long time.
MySQL's Place: Databases and ProgrammingApr 13, 2025 am 12:18 AMMySQL's position in databases and programming is very important. It is an open source relational database management system that is widely used in various application scenarios. 1) MySQL provides efficient data storage, organization and retrieval functions, supporting Web, mobile and enterprise-level systems. 2) It uses a client-server architecture, supports multiple storage engines and index optimization. 3) Basic usages include creating tables and inserting data, and advanced usages involve multi-table JOINs and complex queries. 4) Frequently asked questions such as SQL syntax errors and performance issues can be debugged through the EXPLAIN command and slow query log. 5) Performance optimization methods include rational use of indexes, optimized query and use of caches. Best practices include using transactions and PreparedStatemen
MySQL: From Small Businesses to Large EnterprisesApr 13, 2025 am 12:17 AMMySQL is suitable for small and large enterprises. 1) Small businesses can use MySQL for basic data management, such as storing customer information. 2) Large enterprises can use MySQL to process massive data and complex business logic to optimize query performance and transaction processing.
What are phantom reads and how does InnoDB prevent them (Next-Key Locking)?Apr 13, 2025 am 12:16 AMInnoDB effectively prevents phantom reading through Next-KeyLocking mechanism. 1) Next-KeyLocking combines row lock and gap lock to lock records and their gaps to prevent new records from being inserted. 2) In practical applications, by optimizing query and adjusting isolation levels, lock competition can be reduced and concurrency performance can be improved.
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
AI Hentai Generator
Generate AI Hentai for free.
Hot Article
Hot Tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Safe Exam Browser
Safe Exam Browser is a secure browser environment for taking online exams securely. This software turns any computer into a secure workstation. It controls access to any utility and prevents students from using unauthorized resources.
MantisBT
Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.
SecLists
SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.
ZendStudio 13.5.1 Mac
Powerful PHP integrated development environment
